Y'know those mechanical puzzles made from chain and horseshoes that seem like they should be easy to solve but whose pieces take forever to disentangle? Well, changing an alternator is like messing with one of those for 2 hours. There are just the right protrusions, hoses and wires in the area to ensure that if it's not perfectly rotated and aligned it won't come out.
But, the more challenging the challenge the greater the sense of accomplishment. Also, it cost half what the garage wanted even after buying new socket sets and wrenches. Now I have more tools I can lend out and never see again :)